The present invention relates to surface cleaning apparatus and particularly to such apparatus which employs an air blast pickup head.
In mobile sweepers fro cleaning debris from the surface of, for example, parking lots, roadways or the like, frequently air blast pickup heads are utilized to remove and collect debris from the surface being cleaned. In such systems, a blower forces air to a pickup head such that an air blast sweeps over the surface being cleaned. This loosens debris which is then withdrawn from the pickup head by a suction line returning to the blower input via a debris collection plenum. A sweeper having these basic structural characteristics is disclosed in U.S. Pat. No. 3,512,206 issued to M. W. Young on May 19, 1970.
A sweeper with this type of pickup head depends upon the maintenance of a relatively close coupling of the pickup head to the surface being cleaned such that the blast of air is effectively contained within the cleaning area for loosening and removing debris. In order to permit the ingestion of relatively large articles, at least the leading edge of the pickup head must have some clearance between its lower edge and the surface to be cleaned and preferably, it utilizes a flexible flap along the leading edge which deflects upon contact with an object and permits ingestion of such object. When the flap, however, is momentarily raised, the head is even more susceptible to the escape of air and dust particles which are turbulently circulated by the air stream.
The difficulty of ingesting both small and large particles of debris with a single pickup head has been solved by the structure disclosed in pending U.S. application Ser. No. 412,668 filed Nov. 5, 1973 entitled SURFACE CLEANING PICKUP HEAD by Jack L. Hommes and assigned to the present assignee. With such a system and with conventinal air blast-type pickup heads, the dust escape problem has not heretofore been satisfactorily solved.
Some attempts have beem made to introduce water into the air stream thus coagulating dust particles preventing their dispersing in the air and escaping from the apparatus. Thus, in one effort to control the dust, water was injected into the debris plenum in relatively large volumes to attempt to control the dust. It was found, hwoever, that in order to provide any degree of dust control, the amount of water necessary resulted in the formation of considerable sludge in the debris plenum and in the air flow path which was objectionable.